Fluid bearing gyroscope

ABSTRACT

A frictionless, zero hysteresis two axis angular rate sensor of the gyroscopic type wherein a one piece, disk-shaped rotor, generally of the form of a &#39;&#39;&#39;&#39;checker,&#39;&#39;&#39;&#39; is electrically spun at high speed and hydrodynamically suspended within a correspondingly shaped cavity in a fixed housing, the rotor constituting the total gas bearing surfaces, the armature of the electric rotor spin motor, the armature of electric pick-offs for detecting precession of the rotor, and the armature of an electric torquer for imposing a rate command for control and self-test purposes; the rotor/cavity wall surface interface being so configured as to maximize the radial support stiffness, the stability of the rotor along the spin axis and the sensitivity of the rotor to angular forces at right angles to the spin axis.

United States Patent [191 Duncan et al.

[ Mar. 27, 1973 [54] FLUID BEARING GYROSCOPE [75] Inventors: Damon H.Duncan; Peter E. Jacobson, both of Phoenix, Ariz.

[52] US. Cl ..74/5.6, 74/5.7

hydrodynamically suspended within a correspondingly [51] Int. Cl. ..GOlc19/18 shaped cavity in a fixed housing, the rotor constituting [58]Field of Search ..74/5, 5.5, 5.7, 5.6; 308/9 the total gas bearingsurfaces, the armature of the electric rotor spin motor, the armature ofelectric [5 6] References Cited pick-offs for detecting precession ofthe rotor, and the armature of an electric torquer for imposing a rateUNITED STATES PATENTS command for control and self-test purposes; thero- 3,606,793 9/1971 Johnston ..74 5.7 torNev/it) Wall Surface interfacebeing 80 Configured 88 3,362,231 1/1968 Baldwin et a1. ..74/5 tomaximize the radial support stiffness, the stability of 2,821,859 2/1958 Crockett ..74/5.6 the rotor along the spin axis and the sensitivity ofthe 3,107,540 10/1963 Curriston ..74/5.7 X rotor to angular forces atright angles to the spin axis. 3,365,958 1/1968 Bard et a1. ..74/53,522,737 8/1970 Brenot ..74/5.7 7 Claims, 2 Drawing Figures s h 32 J 38i9 S A 52 Primary Examiner-Manuel A. Antonakas Att0meyS. C. Yeaton [57]ABSTRACT A frictionless, zero hysteresis two axis angular rate sensor ofthe gyroscopic type wherein a one piece, disk-shaped rotor, generally ofthe form of a checker, is electrically spun at high speed andPATENTEDHARZY 1975 W7l/l/Y Y lllllllll l/ I Ill/I PRESSURE FIG.2.

IN VENTORS DAMON H. DUNCAN PETE/P E JACOBSON ATTORNEY FLUID BEARINGGYROSCOPE BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates generally to gyroscopic apparatus and morespecifically to gyroscopic angular rate sensors of the free rotor typefor detecting and measuring angular rates of movements of a vehicle onwhich it is mounted about two orthogonal axes thereof.

The rate sensor of the present invention is of the type wherein a singlerotating element is supported in a frictionless manner with completefreedom about all axes in a closed cavity by the hydrodynamic force offluid, such as air or other gas, set in motion by virtue of the highspeed spinning thereof. As will be explained more fully below, therotor-gas-cavity wall interface is so configured as to provide radial,axial and angular spring forces arranged to radially support thesensitive element and simultaneously to maximize the stability thereofalong its spin axis and yet also to maximize its sensitivity torotational forces at right angles to the spin axis.

2. Description of the Prior Art Conventional gimbal supported rate gyrossuffer from mechanical complexity, rotor unbalance about a constrainedspin axis, friction in the gimbal bearing, misalignments of mechanicaland electrical components, acceleration effects on gimbal suspension,susceptibility to temperature variations and wear, etc., all of whichadversely affects the gyros threshold sensitivity, linearity of itsoutput, zero null, hysteresis characteristic, and useful life.

Gas supported gyro rotors have been heretofore proposed but in manydesigns the gas bearing merely replaces the ball bearings of the rotorand/or the ball or jewel bearings of the gimbal, which while reducingsome of the above effects does not affect others.

Also, so called free rotor or gimballess gyros have been proposed, onetype embodying a gas or liquid supported sensitive element that rotateswith the supporting housing and another type when the rotor is universalmechanical means supported on the end of a support shaft. All of theseschemes suffer from many of the above problems and are exceedinglymechanically complex and hence very costly.

Free spring gas supported rotor rate sensors wherein the gas acts as aspring, similar in some respects to the gyro of the present invention,have been proposed, see for example US. Pat. No. 2,821,859, but thisconfiguration is not practical since it requires external gaspressurization not only to spin the rotor but also to provide itssuspension through gas leakage to the at mosphere. With thisarrangement, the gyro speed and spring constants cannot be optimized orreadily maintained. Furthermore, its washer or torroidal configurationseverely limits its axial to angular stiffness ratio to the point thatits sensitivity to angular rate renders it impractical for high accuracyrate systems. lts complex gas/surface interface increases greatly itsmanufacturing costs. Another disadvantage of this prior configuration isits inability to be externally torqued for command or self-testpurposes.

SUMMARY OF THE INVENTION The rate sensor of the present inventionovercomes and substantially reduces the above disadvantages of knownprior art structures. Its simplicity of mechanical and electrical designgreatly increases its reliability and decreases cost. Basically, thepresent rate gyro sensor is a two axis rate sensor and comprises a rotorhaving the general shape of a checker lapped smooth on all surfaces andcontained within a correspondingly shaped closed cavity in a supportinghousing normally fixed in the aircraft. The cavity is slightly largerthan the rotor and the space therebetween is filled with a suitable gas,which can be air or other gas such as nitrogen, helium, etc. It will beunderstood, however, that the support fluid may be a liquid. The housingincludes the stator of a hysteresis driving motor, the outer peripheralsurface of the rotor constituting the saturable portion of the motorrotor; the arrangement being such that the rotor is driven at high speedabout its axis of symmetry within the cavity, thereby generating thehydrodynamic force which floats the rotor and provides it with fullangular and translational freedom of motion. The housing may, forexample, be a right cylinder, the axis of symmetry of the rotor cavityand the rotor coinciding generally with the axis of symmetry of thehousing. This axis will be referred to as the spin axis. Two orthogonalaxes at right angles to the axis of symmetry constitute the input/outputaxis of the sensor and will be referred to as the x-axis and the yaxiseach of which will be both an input and an output axis. Since the gassystem is closed completely, the gas spring parameters may be preciselyestablished atmanufacture and thereafter maintained. These parametersare in effect spring constants attributable to the stablecharacteristics of gas and the cavity parameters. With thisconfiguration, the hydrodynamic gas pressure provides six primaryrestraints, three translational and three angular all referenced to theabove three primary axes and, in accordance with the teachings of thepresent invention, the mechanical design of the rotor/gas/cavity wallsinterface determines and controls these restraints. The outer peripheralsurface of the checker shaped rotor and its corresponding cavity wallprovide a very high restraint to translational movements of the spinningrotor along the x and y axis. The third translational restraint, i.e.,along the spin axis, is also very high and completely stable. Thisrestraint is critical and is provided by shaping the opposed flatcircular surfaces of the cavity side walls to provide a desired pressureprofile across the diameter of the rotor, i.e., high pressure at thisaxis and dropping off rather rapidly toward the rotor periphery. Thisshaping may take the form of shallow spiral grooves or spiral roughenedsurfaces extending generally radially from a small diameter unshapedarea at the spin axis. The shaping of the spirals is very carefullycontrolled as it is essential in providing the first and second of theabove angular restraints; viz: angular movements about the x and y axes.These angular restraints are critical to the characteristics of the gyroand are very low compared to the axial translational restraint and it isan object of the present invention to maximize and maintain theaxial/angular ratio between these restraints. The third angularrestraint, i.e., about the spin axis, can be made low by reason of thedesign configuration as it acts to retard rotation of the rotor aboutthe spin axis. The gas spring reference is frictionless and contributesto the hysteresisless characteristics of the gyro in responding toangular rates experienced about the input axes.

second pairs of condenser plates, each pair being equally radiallyspaced along the x and y axis respectively of one cavity wall on eachside of the spin axis and suitable electronic circuitry to convert thedifferential capacity change due to angular displacement of the rotorspin axis relative to the cavity wallsinto signals useful for controlpurposes.

The single piece rotor further constitutes the armature of the electrictorque motors by which the rate sensor may be caused to precess to anangular position representative of a commanded rate, a requirement forstable platform applications, for example. Additionally, the torquemotors may be employed to exercise the gyro for self-test purposes, arequirement for present day rate sensors used for control purposes, suchas in automatic stabilization equipment for aircraft. The torque motorsare simply coils mounted in the same orientation as the pick-off platesbut on the opposite wall of the rotor cavity. As will be explainedbelow, the application of a torque signal to the y-axis torquer, forexample, will result in a displacement of the rotor in that axis whichdisplacement represents or simulates a rate input about the x-axis.

Thus, the rate sensor ofthe present invention is unique in that thesingle dynamic element, i.e., the rotor, comprises a single machined andlapped disk having the general shape of a checker, and acts as motorarmature, torquer armature and pick-off armature and has gas bearingsurfaces for hydro-dynamically and hence frictionlessly suspending therotor in a correspondingly shaped housing cavity, wherein theaxialto-angular restraint ratio is maximized and cross coupling effectsare minimized whereby to provide a zero hysteresis, high accuracy, highresponse, long life two-axis rate sensor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view ofthe gyro constructed in accordance with the teachings of the presentinvention; and P faces of thecavity 11 are also lapped smooth, espe- Icially the cylindrical side wall surface 19. The stator windings 22 areaccommodated in the cylindrical opening 23 formed by the outer walls ofend pieces 13 and 14 and reentrant portions 17 and 18 thereof. A spacerelement 24, precisely machined and cooperable with the machine lip ofend portion 14 serves as a motor stator alignment ring whereby theelectric field of the stator may be very accurately aligned with respectto the cavity 1 l and contribute no rotor drive component normal to therotor spin axis. Additionally, an alignment ring 26 is provided so as toenable a precision alignment and spacing of the opposed interiorcircular end walls of the interior cavity 1 l.

The the Xbetween the interior walls of cavity 11 and the external wallsof rotor 10 is filled with a suitable fluid such as a gas, which may beair, nitrogen, heliurn or the like, at a suitable pressure. Thus, withthe rotor 10 being spun at high speeds by motor 21, the gas by virtue ofhydrodynamic forces suspends the rotor 10 within the cavity 11 with fullsix degrees of freedom, three angular and three translational. In otherwords, the gas performs the function of the rotor mount gimbal of aconventional gyroscope without the mechanical and operationaldisadvantages set forth above. At

7 the same time, the compressibility characteristic of the FIG. 2 is adiagram illustrating the rotor/cavity/gas pressure interface of thedevice of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thegyroscopic device of the present invention comprises an inertial elementor rotor 10 which consists of a single or unitary disk, preferably ofhysteresis rotor steel, formed generally in the shape of a conventionalchecker game piece and lapped smooth on its continuous flat end surfacesand its continuous cylindrical surface. The rotor is contained in acorrespondingly shaped cavity 11 within a cylinder-shaped housing 12consisting generally of two end portions .13 and 14. The internal cavityend walls are defined by the end surfaces 15 and 16 of reentrantportions 17 and 18 of end portions 13 and 14, respectively, while thecircular cavity side wall is defined by the inner circular surface 19 ofthe laminated core portion 20 of the stator 21 of a hysteresis drivingmotor the rotor constituting the rotor of the motor. The inner surgas,as will be explained more fully below, provides the spring restraint anddamping required of'a gyroscopic rate sensor.

As shown in FIG. 1, the three major reference axes for the gyro arefixed in the housing and are as follows: the spin axis SA, which in theconfiguration illustrated constitutes the axis of symmetry ofcylindrical housing and cavity; axis X-X orthogonal to the spin axis andin FIG. 1 normal to the plane of the drawing; and axis Y- Y alsoorthogonal to both the spin axis SA and'axis X X; the axes XX and YYconstitutes both input and outputaxes of the sensor as will be explainedbelow.

In normal use, output data proportional to turn rate components aboutthe input axes of the gyro is derived by means of high frequencycapacity pick-up elements and associated electronics. For sensing tiltsof the rotor 10 within cavity 11 about axis XX,'a pair of capacityplates 30 and 31 are mounted in the face 15 of reentrant portion 18 ofend wall 14. These .plates are precisely equally spaced from the spinaxis SA in the secured to end portion l4 and protected from the externalenvironment by a suitable cover or end cap 35. In a similar mannercorresponding capacity plates 36 and 37 (only one of which is shown inthe section of FIG. 1) are provided for detecting tilts of rotor 10about axis YY, the output connections 38 and 39 (only 38 being shown inthe section of FIG. 1) being similarly brought out to the electronicspackage 33. The other elements of thefcapacitive pick-offs 30 and 31comprise the rotor 10 and the housing end walls 15 and 16, the gasconstituting the capacitor dielectric medium. It should be understoodthat other forms of pick-offs may be used without departing from theteachings of the present invention in its broader aspects.

In many applications of the rate sensor of the present invention, it maybe desired to provide an input. rate command function, particularly inconnection with performing preflight or inflight tests of the gyro. Thisis sometimes referred to as a self-test capability. For this purpose,electromagnetic torquer coils are provided and, in the illustratedembodiment, comprise core and winding assemblies 40 and 41 mounted inr'eentrant portion 17 of end portion 13 equally spaced from the spinaxis SA in a direction parallel to axis YY whereby and properlyenergized will produce a torque about this same axis to simulate ahousing rate about axis YY. In a similar fashion corresponding torquercoils 42 and 43 (not shown in the cross-section of FIG. 1) for applyingcommand input torques about axis Y-Y for simulating housing rates aboutaxis XX. Torquer elements 40-43 are maintained in place by clamp plate44. Operation of the sensor in response to an input command through thetorquers will be described below.

In accordance with the principle teachings of the present invention, thehydrodynamic forces generated by the spinning rotor provide all of thegyro support and damping forces and spring restraints required of a ratesensor; that is, to provide the translation and angular restraintsabove-mentioned. It is an objective of the present invention to optimizethese forces in order to provide optiinum sensitivity, damping, andruggedness.

The checker configuration of the rotor substantially reduces any gaspressure restraint'of the rotor to angular motion about the spin axisand provides a substantially frictionless rotary support about adiameter while the hydrodynamic restraints to translational motion ofthe rotor in the plane defined by the XX and YY axes are very highwhereby to provide support against acceleration and shock loads. Therestraints with respect to the remaining axes of freedom are optimizedby the following structure.

It is desired that the translational restraint of the rotor along thespin axis be made very high and very stable so as to in effect provide astable pivot point near to the intersection of theXX and YY axes aboutwhich the rotor may freely rotate, the latter restraint being relativelylow by comparison. The ratio of the latter two restraints, which may bereferred to as the axial to angular spring-rate ratio or stiffnessratio, should be as high as possible. The rotor/gas/cavity configurationof the present invention provides for the optimization of this ratio aswell as the control of the angular stiffness provided by the gas.

Referring now to FIGS. 1 and 2, the desired axial to angular springrestraint is provided by shaping the end walls and 16 so as to provide agas pressure profile across the diameter of the rotor face/end wall gapswhich is very high at the center, i.e., at the spin axis SA, and dropsoff toward the rotor periphery, as illustrated by the pressure curve 49at the right of FIG. 2. The end wall shaping comprises lands and groovesor areas 50 and 51 of different axial profiles. These areas have agenerally spiral configuration emanating from a small diameter unshapedarea near the spin axis and extending outwardly toward and preferablyterminating short of the periphery of the end walls. The actualdimensions and slope of the spiral shaping depends, among other things,upon the normal operating angular velocity of the rotor, the viscosityof the gas and desired axial to angular stiffness ratio. It will beunderstood that the actual groove profile may vary for each applicationand is selected, as stated, to achieve maximum stability of the rotoralong the spin axis and the desired high axial to angular stiffnessratio. Furthermore, sincethe entire gas envelope is closed and sealed,once the parameters are established they are thereafter maintainedsubstantially constant. Additionally, since the gyroscopic rotor of thepresent invention operates ina substantially frictionless environmentand all forces acting thereon are substantially pure forces withoutfriction, the rate sensor is devoid of hysteresis effects.

Having now described the structure of the rate sensor of the presentinvention, the operation thereof will now be discussed under two normaloperating conditions, i.e., upon the sensor housing being subject to arate of turn in inertial space about, for example, the YY axis and upona commanded rate input to, for example, the torque coils 40 and 41.

Assume that the sensor is mounted in an aircraft and that it issubjected to a rate of turn component in inertial space about the YYaxis in say, a clockwise direction looking toward the top of the drawingof FIG. 1. Upon initiation of the turn rate, i.e., a turn acceleration,a moment due to compression of the gas between the rotor face and cavityend walls, will be produced tending to rotate the rotor 10 clockwiseabout the Y- Y axis. This rotation will result in a signal proportionedto turn acceleration being generated by pick-offs 38 and 39. With therotor spinning in the direction of the vector arrow, this moment willproduce a clockwise precession of the rotor 10 about the XX axis in theplane of the page. As the turn rate becomes constant, the precession ofthe rotor 10 about the XX axis causes a CCW gas reaction moment toappear in the XX axis. This reaction moment causes a CW procession ofthe rotor 10 in inertial space about the XX axis which when equal to thecase rotation rate reduces the input moment in the XX axis and theprecession in the YY axis to zero. Under a steady-state turn rate, thegyro rotor 10 assumes a steady-state canted position within the cavity11 about the XX axis, the angular position of which is proportional inmagnitude to this rate of turn about the YY axis. This angulardisplacement will be sensed by differential change in capacitance of thepick-off plates 30 and 31 and the electronics will supply an outputproportional in amplitude to the magnitude of the turn rate and of aphase dependent upon the direction of the turn rate about the YY axis.The same operation occurs for turn rate components about the XX axis.

In modern rate sensor applications it is desired to exercise the sensorfor self-test purposes. Thus, an electrical signal applied to torquercoils 40 and 41, for example, in a direction such as to produce aclockwise torque about the XX axis as viewed in FIG. 1, will effectivelyproduce a counterclockwise gas compression moment on the rotor 10in theX-X axis which is equal to the magnitude and cancels the applied momentand results in an angular displacement of the rotor in the XX axis whichis equivalent to a housing rate input It should be noted that as statedabove, since the initial response of the gyro to a turning moment actingon the aircraft is a turn acceleration and it is reflected in a relationangular movement of the rotor 10 and housing 12 about the gyro inputaxis proportional thereto, this initial movement will result in a signalbeing generated in the pick-off in the input axis proportional to thisturn moment or angular acceleration. In other words, this signal isproportional to the angular acceleration producing the turn rate. Thisangular acceleration signal may also be used for control purposes. Forexample, in an aircraft stability augmentation system for-the yaw andpitch axes of the aircraft this turn acceleration signal could be usedinstead of the turn rate signal since in these axes it is normallydesired to block out the steady state turn rate term. Of course, thenormal turn rate signal from the gyro output axis pickoff could also beused where necessary or a combination of turn acceleration and turn ratesignals suitably filtered, for example, in the yaw axis to damp theclutch roll charac teristics of the aircraft, may be used.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that any changes made within thepurview of the appended claims may be made without departing from thetrue scope and spirit of the invention in its broader aspects.

We claim:

1. A gyroscopic rate sensor comprising a solid disc-shaped rotor havingflat circular end wall surfaces and an interconnecting cylindrical outerperipheral surface,

a housing having a sealed internal cavity, the effective internal wallsurfaces thereof conforming to the external wall surfaces of said rotorbut of slightly larger over-all dimensions and receiving said rotorfreely therein,

a fluid contained within and completely filling the internal cavityspace defined by said rotor and housing walls,

motor means for spinning said rotor about its axis of symmetry tothereby generate hydrodynamic pressure forces between the cavity androtor walls whereby said rotor is supported within said cavity withlimited freedom of translational and precessional motion, and I means inthe interface between the corresponding circular flat end wall surfacesof said rotor'and cavity for increasing the hydrodynamic pressure atsaid axis of symmetry relative to that at the peripheral zone of saidinterface whereby to provide a relatively high ratio of axial to angularhydrodynamic stifiness of said rotor to external axial andangular forcesacting on said housing.

2. The rate sensor as set forth in claim 1 wherein said last-mentionedmeans includes profiled, spiral shaped configurations on one of saidcircular wall surfaces and extending in generally radial directions fromsaid axis of symmetry.

3. The rate sensor as set forth in claim 2 wherein said spiralconfigurations are on the opposed internal circular surfaces of saidhousing.

4. The apparatus as set forth in claim 2 wherein said spiralconfigurations extend from a finite central radius of said circularhousing interior wall faces to a radius spaced a finite distance fromthe periphery thereof.

5. The rate sensor as set forth in claim 1 wherein said motor statorincludes a stator core element having a cylindrical central opening andwhere the internal walls thereof constitutes the cylindrical interiorwall of said cavity.

6. The rate sensor as set forth in claim 1 further including pick-offmeans wherein first and second pairs of pick-off elements are arrangedon said circular housing wall along mutually perpendicular diameters fordetecting angular movements of said rotor within said cavity aboutmutually perpendicular axes orthogonal to said axis of symmetry andparallel to said wall diameters in response to turning forces acting onsaid housing, and

the output of said first pair of pick-off elements being proportional tothe turn acceleration of said housing in response to a turning force andthe output of said second pair of pick-offs being proportional to theturn rate of said housing in response to the same turning force.

7. The rate sensor as set forth in claim 1 further including electricalmultiple part pick-off means and electrical multi-pole part torquermeans wherein said disk shaped rotor constitutes one part of saidpick-off means and said torquer means and the other part of saidpick-off means is supported in one of said circular 'interior housingwalls while the other part of said torquer means is supported in theother one of said circular interior housing walls.

1. A gyroscopic rate sensor comprising a solid disc-shaped rotor havingflat circular end wall surfaces and an interconnecting cylindrical outerperipheral surface, a housing having a sealed internal cavity, theeffective internal wall surfaces thereof conforming to the external wallsurfaces of said rotor but of slightly larger over-all dimensions andreceiving said rotor freely therein, a fluid contained within andcompletely filling the internal cavity space defined by said rotor andhousing walls, motor means for spinning said rotor about its axis ofsymmetry to thereby generate hydrodynamic pressure forces between thecavity and rotor walls whereby said rotor is supported within saidcavity with limited freedom of translational and precessional motion,and means in the interface between the corresponding circular flat endwall surfaces of said rotor and cavity for increasing the hydrodynamicpressure at said axis of symmetry relative to that at the peripheralzone of said interface whereby to provide a relatively high ratio ofaxial to angular hydrodynamic stiffness of said rotor to external axialand angular forces acting on said housing.
 2. The rate sensor as setforth in claim 1 wherein said last-mentioned means includes profiled,spiral shaped configurations on one of said circular wall surfaces andextending in generally radial directions from said axis of symmetry. 3.The rate sensor as set forth in claim 2 wherein said spiralconfigurations are on the opposed internal circular surfaces of saidhousing.
 4. The apparatus as set forth in claim 2 wherein said spiralconfigurations extend from a finite central radius of said circularhousing interior wall faces to a radius spaced a finite distance fromthe periphery thereof.
 5. The rate sensor as set forth in claim 1wherein said motor stator includes a stator core element having acylindrical central opening and where the internal walls thereofconstitutes the cylindrical interior wall of said cavity.
 6. The ratesensor as set forth in claim 1 further including pick-off means whereinfirst and second pairs of pick-off elements are arranged on saidcircular housing wall along mutually perpendicular diameters fordetecting angular movements of said rotor within said cavity aboutmutually perpendicular axes orthogonal to said axis of symmetry andparallel to said wall diameters in response to turning forces acting onsaid housing, and the output of said first pair of pick-off elementsbeing proportional to the turn acceleration of said housing in responseto a turning force and the output of said second pair of pick-offs beingproportional to the turn rate of said housing in response to the sameturning force.
 7. The rate sensor as set forth in claim 1 furtherincluding electrical multiple part pick-off means and electricalmulti-pole part torquer means wherein said disk shaped rotor constitutesone part of said pick-off means and said torquer means and the otherpart of said pick-off means is supported in one of said circularinterior housing walls while the other part of said torquer means issupported in the other one of said circular interior housing walls.